1. Field of the Invention.
The present invention relates to video imaging, in particular, to a computerized video imaging system for analyzing and displaying photographic transparencies for deriving printing illumination values.
2. Description of the Prior Art.
In the field of photographic printing, realistic and aesthetically pleasing photographic prints are produced from transparencies by carefully controlling the variable aspects of the printing process, including the printing illumination. In color printing, the printing illumination can be adjusted to compensate for various deficiencies and excesses in the original transparency. Color-controllable lamphouses are well known and are generally of either the subtractive type wherein filters are employed to block extensive amounts of light of the subtractive primary colors magenta, yellow, and cyan and the additive type wherein separate light sources are provided for the additive primary colors red, green and blue. An example of an additive lamphouse is disclosed in the Van Wandelen U.S. Pat. No. 4,124,292 wherein white output bulbs are provided with filters for producing the desired colors and controlled to provide the desired mix. Analog controls for lamphouses such as potentiometers and the like are known, but such controls require calibration and results tend to vary between different control systems.
Printing illumination systems have also been devised which analyze a transparency and adjust the printing illumination accordingly to produce color prints which fall within certain predetermined "population centers" within which certain types of prints are classified. Such techniques are particularly well adapted for volume color printing operations since they tend to be highly automated and require little, if any, operator input. However, for high quality color photography such as portrait work and the like, trained operators are generally employed for manually adjusting the printing illumination until lifelike and attractive color balances are achieved. A positive image of the transparency may be projected on a color CRT monitor, for example as shown in the Horiguchi et al. U.S. Pat. No. 4,393,398. The operator then adjusts the illumination hue and density levels and observes the effects of such adjustments on the monitor. The operator will often compare the monitor image of the transparency with an existing reference image. Such reference images are generally in printed form and a problem exists in comparing CRT transparency images with photographic printed images. Because of the differences in the two display mediums and the inherent color distortions in the scanning and monitoring system, realistic and aesthetically pleasing photographic prints have been difficult, time consuming and expensive to achieve with prior art printing and analyzing systems.
Heretofore, there has not been available an imaging system which displays a reference image alongside a transparency image on a CRT monitor with the advantages and features of the present invention.